Ion Mihai Pacepa is a high-level Romanian intelligence official who defected to the United States during the Carter admistration. Subsequently, according to his Wikipedia entry, "he worked with American intelligence in various operations against the former Eastern Bloc."

Pacepa has recently expressed his opinions on the Kennedy assassination in a manuscript "Programmed to Kill", quoted in this blog. He maintains that Khrushchev and the KGB programmed Oswald to kill Kennedy but later unsuccessfully tried to abort his mission. In the end Oswald went ahead on his own. His opinion seems to be based more on his professional opinion than on evidence but as an intelligence professional his opinion is one to be taken seriously. (One must also consider the possibility of disinformation. He once worked for the Communist Romanian government, but it is obvious who he is working for now.)

All of us bloc intelligence leaders had spent at least twenty years focused on recruiting American servicemen assigned outside the United States, and all of us could recognize the elements of Oswald’s intelligence handling even in our sleep...It was crystal clear to us that Oswald had been recruited by Soviet espionage while he was a Marine stationed at Atsugi Air Base in Japan ...

I am inclined to agree with him here; however I think that Oswald was probably working for American intelligence at the time.

the U.S. investigators had in their possession Oswald’s 1961 letters to the U.S. Embassy in Moscow and to his brother Robert in the U.S. stating that his wife, Marina, was born in Leningrad; the investigators established that she did indeed speak with a Leningrad accent, but they did not know what to do with Marina’s birth certificate stating that she was born in remote Archangel oblast. The investigators were, evidently, not familiar with the Soviet pattern requiring that intelligence agents selected to become spouses of Western visitors be endowed with fake identity documents showing that they came from remote areas, usually ones prohibited to foreigners, so as to preclude attempts to verify their backgrounds.

Again, I think he is correct than the KGB likely steered Marina toward Lee Oswald.

That was another Soviet pattern—seven chiefs of the Soviet political police itself were secretly or openly assassinated to prevent them from incriminating the Kremlin. Furthermore, immediately upon news of JFK’s assassination Moscow launched Operation “Dragon,” a disinformation effort in which my service was deeply involved. The aim—which has succeeded only too well—was to throw the blame on various elements in the United States for killing their own president.

Pacepa, in these excerpts at least, does not consider the possibility that Oswald was working for American intelligence the whole time, a possibility that any intelligence analyst would obviously have considered.

The only evidence that Pacepa has ever alluded to is a conversation he had with Romanian President Ceausescu, in this article in National Review.

“Ten,” Ceausescu remarked to me. “Ten international leaders the Kremlin killed or tried to kill,” he explained, counting them off on his fingers. Laszlo Rajk and Imre Nagy of Hungary; Lucretiu Patrascanu and Gheorghiu-Dej in Romania; Rudolf Slansky, the head of Czechoslovakia, and Jan Masaryk, that country’s chief diplomat; the shah of Iran; Palmiro Togliatti of Italy; American President John F. Kennedy; and Mao Zedong. (Among the leaders of Moscow’s satellite intelligence services there was unanimous agreement that the KGB had been involved in the assassination of President Kennedy.)

Now it is my opinion that no intelligence service, either theirs or ours, would have used Oswald in a plot to assassination the American President, except as what he said that he was, a "patsy." Although Oswald was hardly the dolt he has been made out to be, neither was he 007. Would the Soviets really have used an individual who could so obviously have been traced back to them? Also it would have been unlikely that either side could be completely sure that he was actually working for them, and had not been doubled.

Is it possible that Pacepa is being influence in his opinions by his current employers in American intelligence? Of late, he has been associated with David Horowitz's FrontPage Magazine and The Washington Times in efforts to establish that Saddam Hussein really did haveWMDs. He also wrote an article for National Review linking John Kerry's Vietnam-era testimony to the Congress to a Soviet propaganda campaign.